Messages in this thread |  | | Date | Sat, 9 Jul 2011 16:29:48 +1000 | | From | Robert Swan <> | | Subject | Re: [bisected] pty performance problem |
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On Sun, Nov 22, 2009 at 09:23:19AM +1100, Robert Swan wrote: > I posted this to the kernel-newbies list, but have graduated to the > adults forum: > > ! Two C programs are having a query-response conversation through a > ! pseudo terminal: > ! > ! A (client) -- forever { send query; read response } > ! B (server) -- forever { read query; send response } > ! > ! Neither has any I/O apart from the pty conversation, so I'd expect to > ! see CPU usage at 100%. When I ran it, the CPU was pretty well idle. > ! After a fair bit of fiddling, it turned out that both sides were > ! taking about 8ms for their read() calls. At that point it seemed > ! pretty clear that this was a delay in the kernel, not the code. > ! > [snip] > > 2.6.31-rc2-00205-gb4b21ca good > 2.6.31-rc2-00206-gd945cb9 bad > > and still bad with the latest: 2.6.32-rc8-00011-ga8a8a66
And still bad with the 2.6.37 release.
I have been using a workaround happily enough, so I'm not nagging. 18 months hardly rates as nagging frequency, possibly sniping, but I'm not doing that either. I tried my test case for the first time in ages today and thought a reminder was merited in case it had slipped between the cracks.
I'll attach the test code, since I didn't post that to the list last time.
Have fun,
Rob. [unhandled content-type:application/x-gtar] |  |